docs: def _get_seqprop_to_seqprop_alignment(self, seqprop1, seqprop2):
          """Return the alignment stored in self.sequence_alignments given a seqprop + another seqprop"""
          if isinstance(seqprop1, str):
              seqprop1_id = seqprop1
          else:
              seqprop1_id = seqprop1.id
          if isinstance(seqprop2, str):
              seqprop2_id = seqprop2
          else:
              seqprop2_id = seqprop2.id
  
          aln_id = '{}_{}'.format(seqprop1_id, seqprop2_id)
  
          if self.sequence_alignments.has_id(aln_id):
              alignment = self.sequence_alignments.get_by_id(aln_id)
              return alignment
          else:
              raise ValueError('{}: sequence alignment not found, please run the alignment first'.format(aln_id))